Final Answer:
ECG machines are calibrated so that: C) 1 cm = 1 mV. Thus the correct option is C.
Step-by-step explanation:
The calibration of ECG machines is standardized to ensure accurate and consistent measurements. In this context, the correct calibration is 1 cm on the ECG paper corresponding to 1 millivolt (mV) in amplitude. This means that the vertical axis on the ECG paper, typically representing voltage, is calibrated such that each centimeter corresponds to 1 millivolt of electrical potential.
This calibration is essential for interpreting the amplitude of the electrical signals recorded by the ECG. Each small square on the ECG paper typically represents 1 mm in both the horizontal and vertical directions. Therefore, with the 1 cm = 1 mV calibration, it becomes easy to measure the amplitude of waves and intervals on the ECG tracing precisely.
In summary, the choice C) 1 cm = 1 mV reflects the standard calibration used in ECG machines, ensuring accuracy in the representation of electrical signals recorded from the heart. This calibration simplifies the interpretation of ECG tracings by providing a standardized and easily interpretable scale for both voltage and time measurements.